You may wonder how some gi can be very inexpensive ($20 range) while others climb up around $100. On the surface they appear to be quite similar. The differences between basic uniforms and pricier ones include thickness of material, brand name, specific design, and more. But one of the most important factors is the time and care put into reinforcing the stitching around the seams.
Most martial arts involve some sort of physical impact or gripping of the gi, but grappling is especially important for judo and jujitsu practitioners. Routinely during workouts their uniforms are gripped, turned, tugged, and pulled. Regular clothing and cheaply made uniforms would get destroyed in a hurry.
Most gi manufacturing companies recognized this problem early on and began constructing higher end uniforms with significantly added attention to the stitching. The areas around the lapel, inseams of the pants, leg cuffs, and sleeves were found to be particularly vulnerable to premature damage. Therefore added material layers were combined with added rows of stitching to form extremely durable and reliable gi construction.
Although I generally recommend having a heavy duty gi on hand, they aren't necessarily ideal for every situation. Sometimes in very hot climates or during long workouts practitioners enjoy the lighter uniforms that can take less abuse but provide much greater ventilation. I believe it's best to have one of both on hand and to use whichever is more appropriate to your situation.